It is the purpose of this project to purify, characterize, and compare tryptophan hydroxylase from several different sources including rat mesencephalic tegmentum and mouse mast cell tumors. One aim of the project is to supply purified tegmental tryptophan hydroxylase for the production of antibodies to be used in studies on tryptophan hydroxylase regulation. A second aim is to determine the biochemical characteristics of tryptophan hydroxylase from such divergent sources as mesencephalic tegmentum, pineal gland, mast cells, and septum, and to detemine the degree of identity between these.